Introduction
State organization is an early indicator of the infant's orientation to the environment, self-regulatory capacities, and cognitive maturation. Premature infants typically exhibit difficulties in regulating sleep and wakefulness. In this study, sleep-wake cyclicity was compared in two groups of premature infants: infants born at very low birthweight (VLBW; 1000-1500 g, n=40) and infants born at extremely low birthweight (ELBW; <1000 g, n=30.).

Method
Trained coders observed the infant's states over four consecutive hours in 10-second frames and marked changes in infant state using a special computerized event-recording program. Observations were conducted for all infants at 37 weeks post-conception age. The following states were coded: quiet sleep, active sleep, transition, cry, unfocused wakefulness, and wakefulness. The relative frequency of each state was compared between the two groups. In addition, state cyclicity was measured using Fast Fourier Transformation (FFT) and the amplitude, number of cycles on the power spectra, and duration of each cycle were compared.

Results
Infants born at extremely low birthweight showed lower proportions of quiet sleep and wakefulness and higher proportion of active sleep. Results of the FFTs showed that the amplitude of sleep-wake cycles were lower in the ELBW, suggesting lower degree of state regulation. There was no indication of the Basic Rest Activity Cycle - a cycle of sleep and wakefulness lasting approximately 45 that is observed in healthy neonates - among the ELBW infants.

Conclusion
The results suggest that, compared to VLBW infants, infants born below 1000 g and before 30 weeks gestation may constitute a special risk group. This group may show more pronounced difficulties in state organization and proper regulation of sleep and wakefulness and these may be associated with specific forms of compromised development.

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